1. Field of the Invention
This invention relates to a network related information transfer method for a connection device such as a routing device (hereinafter referred to as "router") connected to a wide area network whereby network related information can be automatically learned and set, and to a data communication system capable of automatically and readily allocating virtual networks.
2. Description of the Related Art
Conventional routers of this type are connected to a wide area network (hereinafter referred to as "WAN") such as a public network (curcuit switching network) or an ISDN in which account is charged in proportion to the connect time or the quantity of data handled. A router performs call control whereby a line connection with a destination router is established when data is to be actually transferred between LANs and is cut off when there is no data to be transferred.
The call control performed by the router includes the following two functions:
According to the first call control function, the router establishes a line connection with a destination router upon receiving data which should be relayed (hereinafter referred to as "relay data") from a terminal connected to the same LAN. Also, in the case where no relay data is generated for a certain period of time, the router cuts off the line connection. To achieve this call control function, it is necessary that the router acquire the required path information (hereinafter referred to as "routing information" or "network related information") for data relay beforehand. To this end, the router is designed to retain statically set routing information or to dynamically learn the routing information.
According to the second call control function, the router performs a connecting/cut-off operation in accordance with a call control command from a data-originating terminal.
In the case where the routing information is statically set to achieve the first call control function, it is necessary that routing information be set with respect to all connectable networks when the router is installed or the system topology has been changed. Accordingly, the setting operation is complicated, possibly causing erroneous settings.
On the other hand, in the case where the routing information is dynamically learned, it is necessary that connections with all connectable routers should be once effected by a manual procedure when the router is installed or the system topology has been changed. This connection work consumes much labor.
In connection with the second call control function, the router requires a separate communication protocol for performing the connecting/cut-off operation.